Apple have created a page where it provides all the necessary instructions on how to access the contents of your backup stored by iTunes for the iPhone device.
Instructions: https://support.apple.com/en-us/HT204215
However, the contents of the backup such as music, images, SMS, apps, etc., are not available. You will need another application that reads those files and extracts data.
Use one of the applications listed through the Search page at Software Informer.